Yes they do, because their existing roadbeds and other infrastructure are perfectly adequate for 50 MPH freight traffic.
If you tried to bump those speeds up to 80 MPH+ for passengers, the costs go up by an order of magnitude or more.
If you tried to bump those speeds up to 80 MPH+ for passengers, the costs go up by an order of magnitude or more.”
Same can be said about the interstate highway system. Try driving long distances on backroads.